26; 



The less the various nutritive substances are retained and the more 

 soluble their compounds, the more easily they are leached out. At best, they 

 reach the deeper soil layers, and in regions of strong sudden precipitation, 

 they can be carried away. The chlorids present in small amounts in most 

 soils are most easily removed, then the nitrates, later the sulfates. This 

 takes place slowly with carbonates of calcium and magnesia and the phos- 

 phates are the most persistent of all. Chlorids are dangerous for agriculture 

 in regions of very slight precipitation, where they accumulate in low lying 

 places, and produce highly concentrated soil solutions. Under the same con- 

 ditions, the so-called "alkali soils" are produced by carbonates and sulfates. 



The question of nitrogen is the most important. The nitrates are so 

 very soluble that the upper soil layers, containing the superficial roots, can be 

 leached of all their nitrates even if the subsoil contains abundant nitrogen. 

 This can only be made available by means of deeply rooted plants. In the 

 face of general practice, not enough emphasis can be laid on the great losses 

 occurring with unsuitable fertilization of the fields. Of the calcium salts, 

 gypsum must be considered since it contains sulfuric acid. With calcium 

 carbonates in damp cHmates, even on soils made from disintegrated lime 

 stone, the calcium content may be poor because the carbonate is slowly 

 leached out^ On the other hand, all the potassium phosphates as well as 

 the phosphoric compounds (with the exception of the alkalis) belong among 

 the most persistent minerals. An exception takes place only in soils with 

 free humic acids. Here the phosphates and also the iron compounds be- 

 come soluble and even the resistant silicates are decomposed and carried over 

 in a soluble form. In this way moor soils are exhausted of all their mineral 

 elements, excepting quartz. 



The natural process of enrichment of the soil by weathering and by the 

 action of wind in moving soil masses, by the decay of organic substances, 

 etc., which effectively counteract leaching, is of value only in long-lived 

 plantations. Here the fact, that the deep growing roots get the nutritive sub- 

 stances from the subsoil, again made available for the upper soil layers by the 

 falling of the leaves, is surely of great importance. In our plantations of 

 one and two-year old plants, we find this help only in the use of green 

 manuring. 



Finally, soil impoverishment from draining must not be passed over. 

 However useful this practice is, as already acknowledged under soil aeration, 

 in places it can act most injuriously. This refers especially to the leaching 

 of nitrates from the soil in localities, where the fertilizer cannot be exten- 

 sively supplied. Naturally the loss reaches a significant amount where an 

 abundant supply of nitrogen is present, as is shown, for example, in Levy's 

 analyses of the drain water from the Parisian sewage fields-. In a liter of 



1 (If water containing- carbon dioxid comes in contact with calcium carbonate 

 it forms calcium bicarbonate, wliicli is mucli more soluble and passes off in the 

 drainage waters. This always occurs in soils containing organic matter. — H. S. R.) 



2 Wollny, E., Die Zersetzung der organischen Stoffe, etc. Heidelberg 1897, p. 4. 



